Hydroxy acids (HAs) and retinoids have been proven to deliver cosmetic benefits, such as improvement in the appearance of photodamaged or naturally aged skin, skin lightening, treatment of age spots, etc. Unfortunately, their use at high concentrations may occasionally be associated with skin irritation, e.g., skin redness and stinging sensation upon application. The irritation can be ameliorated by lowering the amount of an active ingredient in the composition or by reducing the active's penetration through the skin. A serious drawback of both approaches is that the efficacy is impaired. The HA related irritation can be reduced by raising the composition's pH but this method yields reduced efficacy due to a decreased HA penetration through the skin. It is desirable to reduce or eliminate the irritation potential of HAs and/or retinoids while maintaining their efficacy.
Turmeric is a powdered rhizome of the plant Curcuma longa Linn. The biological activities of turmeric have generally been attributed to curcumin, a component of turmeric extract. Curcumin has been reported to have anti-inflammatory and anti-oxidant activity. See Huang et al., "Inhibitory Effects of Curcumin on Tumorigenesis in Mice", Journal of Cellular Biochemistry Supplement 27:26-34 (1997), Mukundan et al., "Effect of turmeric and curcumin on BP-DNA adducts", Carciogenesis, Vol. 14, No. 3, pp. 493-496 (1993) and Huang et al., "Inhibitory Effects of Curcumin on in Vitro Lipoxygenase and Cyclooxygenase Activities in Mouse Epidermis", Cancer Research 51, 813-819 (1991).
U.S. Pat. No. 5,053,222 (Takasu et al.) discloses a hair cosmetic composition for dandruff treatment which may contain a variety of optional ingredients, including certain alpha-hydroxy acids, vitamin A, and turmeric. U.S. Pat. No. 5,152,983 (Nambudiry et al.) discloses sunscreen compositions comprising a 1,3-diketone, which may be curcumin. The 1,3-diketone is present in the Nambudiry composition at 0.01 to 15%. By contrast, the curcumin content in the compositions of the present invention, even if up to 20% of turmeric extract is used, is at most 0.0002%, i.e., orders of magnitude below the minimum amount in the Nambudiry patent. If turmeric extract were used at levels sufficient to provide curcumin amount of Nambudiry patent, unacceptable yellow color would result.
The art discussed above does not teach any compositions containing turmeric extract at a level presently claimed in combination with HAs and/or retinoids. The art does not appear to teach the use of turmeric extract or curcumin to reduce irritation or sting associated with the use of HAs and/or retinoids. Even more importantly, the art does not disclose the criticality of employing turmeric extract rather than curcumin, to reduce skin irritation. On the contrary, the literature appears to equate the activities of turmeric extract and curcumin.